Hollow-tubed systems are used in a variety of applications. For example, Electrical Metallic Tubing (“EMT”) conduit systems include elongate, thin walled, non-threaded tubes that are usually formed of metal. EMT tubes are used to enclose electrical wires therein. Similar systems include Rigid Metal Conduit (“RMC”), Galvanized Rigid Conduit (“GRC”), Intermediate Metal Conduit (“IMC”), Polyvinyl Chloride (“PVC”) conduit, Armored Cable (AC (BX)), Metal Clad Cable (MC), Flexible Metal Cable (FMC), Flexible Metallic Liquid Tight Conduit and Non-Metallic Liquid Tight Conduit. Although often formed from metal, other materials such as plastic, fiber or fired clay can be used as well.
A typical EMT, RMC, or other conduit system usually includes electrical junction boxes, a plurality of EMT tubes, and other electrical or mechanical elements that are joined together with fittings or couplings to provide a continuous protected chamber for receiving and enclosing electrical wires and their connections. These fittings or couplings join the tubes to the junction boxes, and also may be used to join two or more sections of tubes together within a junction box.
Currently, fittings or couplings for joining certain of these elements have important limitations that render conventional approaches inadequate and/or less than optimal. For example, one common fitting includes a connector body with an internally threaded compression nut screwed onto a body of a fitting having external male threads. The end portion of a tube/conduit is slidably received within the compression fitting, and a worker must tighten the compression nut to compress a steel gland ring that is pre-installed between a compression fitting body and compression nut in order to secure the tube within the fitting. While useful in theory, in practice this design has disadvantages. For example, workers can over-tighten the compression nut sufficiently to strip both female and male threads of a compression fitting; this usually leaves a tube not secured or not locked in the desired position created by the compression fitting. Alternatively, a worker can under-tighten a compression nut to the male threads of a compression fitting, thereby allowing the tube to become disconnected over time and expose the wiring that within the tube.
In some cases, when an exterior thread on a compression fitting body or interior thread on a compression nut are not threaded or machined properly, the exterior threads on the compression fitting body and interior threads on the compression nut will not engage or mate well. This misalignment can cause scraping along the entire compression fitting or a loose connection, thereby allowing the tube/conduit to become disconnected over time and expose the wiring within the tube.
Another common type of fitting includes a body with a perpendicularly mounted threaded set-screw. The end portion of a tube is slidably received within the body of a set screw fitting, and a worker must tighten the set screw to secure the tube within the fitting. While satisfactory in principle, in practice, workers may over tighten the set-screw, thereby placing excessive pressure on a localized portion of the tube. In some cases, this excessive pressure can damage or even pierce the tube. Further, over-tightening one or two set-screws can strip the female threads in the screw boss. Alternatively, a worker can under-tighten the set-screw, thereby allowing the tube to become disconnected over time and expose the wiring within the tube.
A typical conduit system can include hundreds of these fittings, all of which require hand tightening of each compression nut and set screw on each fitting. The labor of performing this repetitive task can increase the overall cost of a project and because of its repetitive nature, may be the source of improperly connected tubes, conduits, or junction boxes.
On the manufacturing side, it is necessary to make millions of the pieces that are part of these fittings; this typically requires a section of tube cut into a defined length to form a compression nut. After forming the compression nut, manufacturing workers tap each nut with internal threads. In addition to forming and adding threads to the compression nut, manufacturing a fitting requires that each nut be secured to a compression connector or to a compression coupling. Further, each compression connector or compression coupling is formed in a similar manner, with threads being formed on one end of each connector and two threads being formed on each compression coupling. The number of stages in the overall manufacturing process, combined with the associated costs in terms of material and energy is relatively high and may be difficult to justify for a less than optimal end product in some use cases.
Set-screw type connectors or couplings require labor to punch holes and tap threads on each screw hole, thereby increasing the cost of production. Millions of set-screw fittings and compression fittings (including the compression nuts) are currently manufactured each year. With each type of fitting being large and relatively heavy, there is a relatively large amount of energy used in the manufacture and distribution (including transportation related expenses) of these fittings. Another impact of the manufacture of conventional fittings of the types described arises because, typically, the couplings are zinc plated. Given the relatively large size of conventional couplings and the number manufactured, this means that a large amount of zinc plating is performed; this may have adverse effects on the environment.
Some efforts have been made to provide a snap-in securing system for joining armored MC, AC (BX) and FMC cables to junction boxes and the like. Examples of these types of systems are found in U.S. Pat. No. 3,272,539 to R. W. Asbury, Sr.; U.S. Pat. No. 3,858,151 to Paskert; U.S. Pat. No. 6,670,553 to Gretz; and U.S. Pat. No. 6,939,160 to Shemtov. Among the disadvantages of such conventional snap-in systems is that these systems cannot bear a significant weight or uncoupling force because the snap-in components are made from spring steel formed into tabs or snap clips, and these tabs or clips engage a portion of the surface of the armored MC, AC (BX), and FMC cables. As a result, in some applications such snap-in systems cannot be used on EMT, RMC, RGC or IMC conduits or tubing because the design of these taps or clips cannot prevent EMT, RMC, GRC or IMC conduits from being pulled out of the snap-in systems when a force is applied to the connectors.
Conventional snap-in fittings typically include a ferrule with one or more annularly mounted tabs or cantilevered snap clips extending therefrom. As mentioned, conventional snap-in systems are designed to be used on MC, AC(BX), and FMC cables; such cables are typically formed from a coil of strip metal to produce an armored exterior surface with wires or cables protected inside the armored surface. The armored exterior surface may have the shape of external threads with a relatively large gap between two threads. When the armored cables are inserted into the snap-in connectors, the tabs or clips are designed to open. The tabs or clips stick out against the ends of the armored cables and snap onto the external threads of the armored cables to prevent the cables from being pulled out of the connector. Note that the tabs or snap clips operably engage only a portion of the surface of the armored MC, AC (BX), or FMC cable(s) inserted into the connector. While these conventional systems may prevent the need for set-screws in some fittings, they can become loose over time and they fail to provide a way to assure that they are properly aligned when installed.
Despite the availability of several conventional forms of tubing joining systems, there remains a need for a quick-connecting tube engaging and joining system that assists in obtaining the proper alignment of each tube and operates to more evenly distribute the securing load around the entire circumference of a tube instead of to a localized region. This attachment technique provides a more secure and properly aligned method of joining two hollow tubes or conduits together and/or joining a hollow tube or conduit to a junction box or other receptacle. Note further, that by distributing the securing load around the circumference of a tube, less stress is put on the tube surface and connecting elements, thereby reducing potential sources of breakage, damage, faults, or other types of failures.
In addition, there remains a need for a tubing joining system that can provide effective and reliable continuity of electricity or electrical signals from a quick-lock connector to a junction box or from a quick-lock coupling to two or more sections of tubes that are part of a system of tubes, conduits, and junction boxes.
Further, there remains a need for a tubing joining system that includes a securing fitting that is substantially less likely to be over-tightened or under-tightened than conventional devices, but instead consistently provides a more optimal securing force at each connection point or region. This aspect operates to save time during installation, reduce the effort used in the installation process, and reduce the breakage of parts. As an additional benefit, the manufacturing and on-site installation phases for the inventive system and methods are relatively environmentally friendly compared to many conventional approaches.
Embodiments of the invention overcome these limitations or disadvantages of conventional systems for coupling tubes or conduits to junction boxes, either alone or in combination.